It means decisions made by 1/2 players usually don't make a whole lot of sense.

They have silly ranges. They pick poor spots to bluff (case-in-point if your opponent bluffed this river).  Him leading flop with extremely strong hands makes no sense either.  You open-raised, you have position, and you will likely be c-betting a good amount of the time.  He wouldn't want to blow you off any bluffs or marginal hands you might be betting.  

The thing is there are so many different player types at 1/2.   Your opponent might be very aggressive in which case he could be trying to win the pot with a very wide range of hands--from semi bluffs (of which there are countless given this board texture) to pure bluffs such as AJ, ATs, KJs, etc.  Such a player's range would be heavily weighted to non-value and he would pretty infrequently have a Q.  Another player-type would be the old man nit.  He probably has a good, but vulnerable hand, and is leading because he's afraid of being sucked out on.   A third player type could be some amalgamation of 1 and 2, not good, but somewhat more balanced.  He'd probably lead top pair sometimes, again because he's afraid of the suck-out, but he may also have some strong draws.  Lots of these players are positionally unaware so it's hard to say whether they recognize that your raise from early position and call OTF is quite strong.  That also is what would make a bluff so bad.  Your worst hands are what?  AJs?  AKo?  99?  Even 99 probably calls here, and so the vast majority of your range defends vs a river bet.

There's also the fact that the player checked the turn.  That could mean anything depending on which player type we're talking about and their level of awareness.  Player 1 could be checking because he took a stab at the pot and is now giving up.  Player 2 could be checking because he's scared, or for pot-control.  Player 3 could be checking because he doesn't want to get blown off of a high-equity draw.   Player 1 might want to see what you do on the turn.  If you check, maybe he thinks that gives him the green-light to bluff on the river.  Who can imagine what goes through the minds of a 1/2 player.  Their strategies never seem to be fully coherent.  I think one thing we can almost entirely rule out by the turn however are nutted hands.  There is just no version of your opponent leading say, a set, getting a call, and then checking this turn.  Beyond that, and I know this is pretty shitty analysis, but an unknown 1/2 player can pretty much be playing these streets the way that they do for any random reason.

I'll conclude with this though.  Once you take into consideration common pre-flop calling ranges at 1/2, the quality of play at 1/2, this specific board texture, and the way the hand played out, it's plain to see that the overall liklihood of your opponent having you beat isn't great enough to justify folding.